United States Patent Application Publication US 2006/0279284 by J. Thomas Vaughan Jr. published Dec. 14, 2006, titled “Wirelessly coupled magnetic resonance coil,” and is incorporated herein by reference. In this document Vaughan describes a radio frequency magnetic coil is coupled to a wireless communication circuit. The wireless communication circuit allows control or monitoring of individual channels or other functions of a coil.
United States Patent Application Publication US 2009/0237077 by J. Thomas Vaughan published on Sep. 24, 2009, titled “RF COIL FOR IMAGING SYSTEMS AND METHODS OF OPERATION,” is incorporated herein by reference. This publication describes an RF coil system for magnetic resonance applications that includes a multi-channel RF coil transceiver and a multi-channel RF coil. The RF coil system is structured for reconfiguration among a plurality of operational modes.
United States Patent Application Publication US 2009/0115417 by Akgun, et al. published on May 7, 2009, titled “Three dimensional RF coil structures for field profiling,” is incorporated herein by reference. This publication details that in one illustrative embodiment, a radio frequency (RF) coil is disclosed. The RF coil may include a plurality of transmission line elements, wherein at least one of the plurality of transmission line elements may have at least one dimension different than a dimension of another one of the plurality of transmission line elements. In some cases, each of the transmission line elements may include a signal line conductor and a ground plane conductor separated by a dielectric.
PCT Patent Application PCT/US2009/060841 was filed by Vaughan et al. on Oct. 15, 2009, is titled “COIL ELEMENT DECOUPLING FOR MRI,” and is incorporated herein by reference. In this document, Vaughan et al. describe an RF coil adjacent an imaging region includes a plurality of conducting coil elements, with each conducting coil element including a proximal portion and a distal portion. The RF coil also includes a capacitance between the distal portions of the at least two conducting coil elements. A mutual coupling inductance between at least two conducting coil elements of the plurality of conducting coil elements is substantially cancelled by the capacitance between the distal portions of the at least two conducting coil elements.
U.S. Pat. No. 7,268,554 issued to Vaughan on Sep. 11, 2007, titled “RF coil for imaging system,” is incorporated herein by reference. In this patent, an RF coil suitable for use in imaging systems is described, which coil has a dielectric filled cavity formed by a surrounding conducting enclosure, the conducting enclosure preferably being patterned to form continuous electrical paths around the cavity, each of which paths may be tuned to a selected resonant frequency. The patterning breaks up any currents induced in the coil and shortens path lengths to permit higher frequency, and thus higher field strength operation. The invention also includes improved mechanisms for tuning the resonant frequency of the paths, for selectively detuning the paths, for applying signal to the coil, for shortening the length of the coil and for controlling the field profile of the coil and the delivery of field to the object to the image.
U.S. Pat. No. 6,633,161 issued to Vaughan, Jr. on Oct. 14, 2003, titled “RF coil for imaging system,” is incorporated herein by reference. In this patent, an RF coil suitable for use in imaging systems is provided which coil has a dielectric filled cavity formed by a surrounding conducting enclosure, the conducting enclosure preferably being patterned to form continuous electrical paths around the cavity, each of which paths may be tuned to a selected resonant frequency. The patterning breaks up any currents induced in the coil and shortens path lengths to permit higher frequency, and thus higher field strength operation. The invention also includes improved mechanisms for tuning the resonant frequency of the paths, for selectively detuning the paths, for applying signal to the coil, for shortening the length of the coil and for controlling the field profile of the coil and the delivery of field to the object to the image.
U.S. Pat. No. 5,557,247 issued to Vaughan, Jr. on Sep. 17, 1996, titled “Radio frequency volume coils for imaging and spectroscopy,” is incorporated herein by reference. This patent describes a distributed impedance circuit MR coil design comprised of a transmission line tunable cavity resonator which is well suited for but not limited to use at high frequencies and for large volumes such as in high field (e.g., 4.1 tesla) clinical MR applications. The distributed circuit transmission line resonator is designed for high frequency, large conductive volume applications where conventional lumped element coil designs fail. A resonant coaxial cavity is variably tuned to the Larmor frequency of interest by tunable transmission line elements. The resonator is effective for large head and body sized volumes, high efficiencies, and broad tuning ranges to frequencies of 500 MHz. The B1 homogeneity of the resonator is a function of the electromagnetic properties of the load itself. Maxwell's equations for the fully time-dependent B1 field predicts “coil” homogeneity with finite-element models of anatomic structure. Coil design and construction, and methods of quadrature driving and double tuning the transmission line resonator, are set forth.
U.S. Pat. No. 5,744,957 issued to Vaughan, Jr. on Apr. 28, 1998, titled “Cavity resonator for NMR systems,” is incorporated herein by reference. In this patent, a cavity resonator is disclosed for use in nuclear magnetic resonance (NMR) systems. The resonator has a housing defining a cavity having a selected length and cross-sectional shape. A layer of electrically conductive material is provided around at least a portion of the housing enclosing a dielectric material (air, gasses, Teflon®, etc.) and the cavity is energized at a Larmor radio frequency useful for NMR systems. The cavity, i.e., a volume enclosed by conductive walls, furthermore, is dimensioned to resonate at the selected radio frequency to thereby generate an alternating magnetic field through the cavity. An opening in the housing is adapted to be placed adjacent an object to be analyzed.
U.S. Pat. No. 5,886,596 issued to Vaughan, Jr. on Mar. 23, 1999, titled “Radio frequency volume coils for imaging and spectroscopy,” is incorporated herein by reference. This patent describes an electromagnetic shield for an NMR radio frequency coil designed to resonate at a selected Larmor frequency. The shield includes an electrically conductive layer surrounding the coil. This electrically conductive layer has a thickness substantially the same as one skin depth at the selected Larmor frequency. As such, the conductive layer efficiently conducts radio frequency currents at the selected Larmor frequency thereby conducting and containing the radio frequency coils at the selected Larmor frequency within the coil. Simultaneously, an electrically conductive layer, due to its thinness, very inefficiently conducts eddy currents of the type induced by the lower frequency DC gradient current switching transients the gradients are utilized to magnetically localize an image slice or volume. Consequently, the conductive layer simultaneously attenuates low frequency eddy current propagation of the type induced by the switching field gradient currents in the NMR application, and therefore does not substantially shield or affect the gradient fields across the coil.
U.S. Pat. No. 7,800,368 issued to Vaughan, et al. on Sep. 21, 2010, titled “High field magnetic resonance,” is incorporated herein by reference. In this patent, a magnetic resonance system is disclosed. The system includes a transceiver having a multichannel receiver and a multichannel transmitter, where each channel of the transmitter is configured for independent selection of frequency, phase, time, space, and magnitude, and each channel of the receiver is configured for independent selection of space, time, frequency, phase and gain. The system also includes a magnetic resonance coil having a plurality of current elements, with each element coupled in one to one relation with a channel of the receiver and a channel of the transmitter. The system further includes a processor coupled to the transceiver, such that the processor is configured to execute instructions to control a current in each element and to perform a non-linear algorithm to shim the coil.
U.S. Pat. No. 6,788,056 issued to Vaughan, et al. on Sep. 7, 2004, titled “Radio frequency magnetic field unit with aperature [sic],” and is incorporated herein by reference. In this document, Vaughan et al. describe an apparatus comprises a radio frequency magnetic field unit to generate a desired magnetic field. In one embodiment, the radio frequency magnetic field unit includes a first aperture that is substantially unobstructed and a second aperture contiguous to the first aperture. In an alternative embodiment, the radio frequency magnetic field unit includes a first side aperture, a second side aperture and one or more end apertures. In one embodiment of a method, a current element is removed from a radio frequency magnetic field unit to form a magnetic field unit having an aperture. In an alternative embodiment, two current elements located opposite from one another in a radio frequency magnetic field unit are removed to form a magnetic filed unit having a first side aperture and a second side aperture.
U.S. Pat. No. 6,958,607 issued to Vaughan, et al. on Oct. 25, 2005, titled “Assymetric [sic] radio frequency transmission line array,” is incorporated herein by reference. In this document, Vaughan et al. describe an apparatus comprises a radio frequency magnetic field unit to generate a desired magnetic field. In one embodiment, the radio frequency magnetic field unit includes a first aperture that is substantially unobstructed and a second aperture contiguous to the first aperture. In an alternative embodiment, the radio frequency magnetic field unit includes a first side aperture, a second side aperture and one or more end apertures. In one embodiment of a method, a current element is removed from a radio frequency magnetic field unit to form a magnetic field unit having an aperture. In an alternative embodiment, two current elements located opposite from one another in a radio frequency magnetic field unit are removed to form a magnetic filed unit having a first side aperture and a second side aperture.
U.S. Pat. No. 7,023,209 issued to Zhang, et al. on Apr. 4, 2006 titled “Method and apparatus for magnetic resonance imaging and spectroscopy using microstrip transmission line coils,” and is incorporated herein by reference. In this document, Zhang et al. describe an apparatus and method for MRI imaging using a coil constructed of microstrip transmission line (MTL coil) are disclosed. In one method, a target is positioned to be imaged within the field of a main magnetic field of a magnet resonance imaging (MRI) system, a MTL coil is positioned proximate the target, and a MRI image is obtained using the main magnet and the MTL coil. In another embodiment, the MRI coil is used for spectroscopy. MRI imaging and spectroscopy coils are formed using microstrip transmission line. These MTL coils have the advantageous property of good performance while occupying a relatively small space, thus allowing MTL coils to be used inside restricted areas more easily than some other prior art coils. In addition, the MTL coils are relatively simple to construct of inexpensive components and thus relatively inexpensive compared to other designs. Further, the MTL coils of the present invention can be readily formed in a wide variety of coil configurations, and used in a wide variety of ways. Further, while the MTL coils of the present invention work well at high field strengths and frequencies, they also work at low frequencies and in low field strengths as well.
U.S. Pat. No. 6,969,992 issued to Vaughan, et al. on Nov. 29, 2005, titled “Parallel transceiver for nuclear magnetic resonance system,” is incorporated herein by reference. This patent describes an excitation and detection circuit having individually controllable elements for use with a multi-element radio frequency coil. Characteristics of the driving signal, including, for example, the phase, amplitude, frequency and timing, from each element of the circuit is separately controllable using small signals. Negative feedback for the driving signal associated with each coil element is derived from a receiver coupled to that coil element.
U.S. Pat. No. 7,710,117 issued to Vaughan, et al. on May 4, 2010, titled “Multi-current elements for magnetic resonance radio frequency coils,” is incorporated herein by reference. This patent describes a current unit having two or more current paths that allow control of magnitude, phase, time, frequency and position of each of element in a radio frequency coil. For each current element, the current can be adjusted as to a phase angle, frequency and magnitude. Multiple current paths of a current unit can be used for targeting multiple spatial domains or strategic combinations of the fields generated/detected by combination of elements for targeting a single domain in magnitude, phase, time, space and frequency.
U.S. Pat. No. 7,514,926 issued to Adriany, et al. on Apr. 7, 2009, titled “Spatially reconfigurable magnetic resonance coil,” is incorporated herein by reference. This patent discusses, among other things, a system and method for a coil having a plurality of resonant elements and an adjustable frame. A position of at least one resonant element can be adjusted relative to at least one other resonant element. A variable impedance is coupled to adjacent resonant elements and the impedance varies as a function of a separation distance. Cables are coupled to each resonant element and are gathered at a junction in a particular manner.
U.S. Pat. No. 7,598,739 issued to Vaughan, Jr., et al. on Oct. 6, 2009, titled “Radio frequency gradient, shim and parallel imaging coil,” is incorporated herein by reference. This patent describes a plurality of linear current elements that are configured about a specimen to be imaged. A current in each current element is controlled independent of a current in other current elements to select a gradient and to provide radio frequency shimming. Each current element is driven by a separate channel of a transmitter and connected to a separate channel of a multi-channel receiver. The impedance, and therefore, the current, in each current element is controlled mechanically or electrically.
U.S. Pat. No. 7,633,293 issued to Olson, et al. on Dec. 15, 2009, titled “Radio frequency field localization for magnetic resonance,” is incorporated herein by reference. This patent describes that technology for controlling non-uniformity in the B1 field includes selecting the phase, magnitude, frequency, time, or spatial relationship among various elements of a multi-channel excitation coil in order to control the radio frequency (RF) power emanating from the coil antenna elements. Non-uniformity can be used to steer a constructively interfering B1 field node to spatially correlate with an anatomic region of interest. A convex (quadratically constrained quadratic problem) formulation of the B1 localization problem can be used to select parameters for exciting the coil. Localization can be used in simulated Finite Difference Time Domain B1 field human head distributions and human head phantom measurement.
U.S. Pat. No. 6,495,069 issued Dec. 17, 2002 to Lussey et al. titled “Polymer composition,” is incorporated herein by reference. Lussey et al. describe a polymer composition comprises at least one substantially non-conductive polymer and at least one electrically conductive filler and in the form of granules. Their elastomer material was proposed for devices for controlling or switching electric current, to avoid or limit disadvantages such as the generation of transients and sparks which are associated with the actuation of conventional mechanical switches. They described an electrical conductor composite providing conduction when subjected to mechanical stress or electrostatic charge but electrically insulating when quiescent comprising a granular composition each granule of which comprises at least one substantially non-conductive polymer and at least one electrically conductive filler and is electrically insulating when quiescent but conductive when subjected to mechanical stress. They did not propose a means for electrically activating such switches.
There is a long-felt need for components having resistance, inductance, and/or capacitance values that are variable under electrical control and are compatible with being operated in extremely high electromagnetic fields.